In the electrolysis of lead-bismuth alloy, insoluble ingredients of the anodes settle to the bottom of the electrolyzer as anode slimes. When anodes are replaced, anode slimes are recycled from the electrolyzer. In electrolysis, base metals with relatively negative potential enter into the solution, whereas noble metals, scarce metals (such as selenium, tellurium, bismuth, etc.), anode powders and the like form insoluble anode slimes. The composition and yield of the anode slimes are mainly related to anode composition, ingot quality and electrolytic conditions.
The yield of anode slimes is generally 0.2-1%, the main components are as follows, Cu: 10-35%; Ag: 1-28%; Au: 0.1-0.5%; Se: 2-23%; Te: 0.5-8%; S: 2-10%; Pb: 1-25%; Ni: 0.1-15%; Sb: 0.1-10%; As: 0.1-5%; Bi: 0.1-1%; trace platinum family metals; and H2O: 25-40%. Platinum group metals, gold, most of copper and a small amount of silver are present in metallic state; while selenium, tellurium, most of silver and a small amount of copper and gold are present as metal selenides and tellurides, such as Ag2Se, Ag2Te, CuAgSe, Au2Te and Cu2Se; and a small amount of silver and copper is present as AgCl, Cu2S and Cu2O. The remaining metals are mostly present as oxides, complex oxides, or arsenates or antimonates.
Anode slime processing mainly involves two categories, i.e. fire method and wet method. The fire method involves calcining lead anode slimes at high temperatures followed by electrolytic preparation. The wet method involves solution extraction and separation.
In the process of high lead-bismuth-silver alloy electrolysis, as thickness of the anode slimes increases rapidly, serious problems of rich lead and lean lead arise inside and outside the anode slimes of the anode, respectively, followed by problems such as decreasing of lead ions, rising of cell voltage and precipitating of impurities, all of which affect the normal operation of electrolysis and quality of the products. Thus, it is necessary to add a lot of yellow lead to the electrolytic system to increase the content of lead ions, in order to solve the problem of “lean lead” in electrolysis. With the smelting of anode slimes, the rich leads inside the anode slimes move on to bismuth-silver smelting Section, which greatly extends the cycle of oxidation refining of the silver smelting section and increases the amount of early slags.